Fluorescent glow discharge lamp



July 19, 1960 F. SCHONHERR FLUORESCENT GLOW DISCHARGE LAMP Filed Feb.19, 1958 lnven tov.

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United States Patent FLUORESCENT GLow DISCHARGE LAMP Fritz Schiinherr,Berlin-Dahlem, Germany, assignor to Patent-Treuhand-Gesellschaft fiirelektrische Gluhlampen m.b.H.

Filed Feb. 19, 1958, Ser.No. 716,141

Claims priority, application Germany Mar. 28, 1957 5 Claims. (Cl.313-217) This invention relates to glow discharge lamps of the typehaving a luminescent coating on the inner wall of the glass bulbenclosing the discharge, and having wire type electrodes which are ofsimple linear shape, i.e., which do not have a spiral r annular shape.Such lamps are quite important for signalling purposes where clearsignal colors are desired which may be readily distinguished from eachother.

It is well known to employ for signalling or indicating purposesminiature type fluorescent glow discharge lamps comprising a smallelongated or tubular glass bulb pro vided with an internal coating ofluminescent material and containing a gas filling essentially of neontogether with a small quantity of mercury and having cold electrodes inthe form of short cylinders or lengths of wire sealed into one end ofthe bulb and extending thereinto in more or less parallel side-by-siderelation in a direction longitudinally of the bulb axis toward the bowlend of the bulb. Such type glow discharge lamps, however, have beencharacterized by a relatively low luminous intensity, as 'a result ofwhich they have been limited in the amount of socalled end-on lightavailable for signalling and indicat ing purposes, that is, the amountof light obtained on the top or bowl end of the bulb opposite the baseor terminal end thereof. While it is possible to increase the luminousintensity of the lamp solely by increasing its power consumption,nevertheless such a manner of obtaining increased luminous intensity hasbeen uniformly avoided up to the present time for the reason that itcauses too much sputtering of the electrode material with resultantdarkening of the fluorescent material on the lamp bulb.

It is an object of my invention, therefore, to provide a fluorescentglow discharge lamp of the character referred to having increasedluminous intensity on the bowl end of the bulb as compared to thatheretofore obtainable for the same power consumption by the lamp.

Further objects and advantages of my invention will appear from thefollowing detailed description of species thereof and from theaccompanying drawing.

In the drawing,

Fig. 1 is an elevation, partly in section and on an enlarged scale, of afluorescent glow discharge lamp comprising my invention.

Fig. 2 is an elevation, partly in section, of the lamp shown in Fig. 1,taken at right angles thereto.

Fig. 3 is a sectional view on the line 3-3 of Fig. 1.

Fig. 4 is an elevation, partly in section and on an enlarged scale, of amodified form of fluorescent glow discharge lamp comprising myinvention, and

Fig. 5 is a sectional view on the line 55 of Fig. 4.

According to the present invention, an increase in the luminousintensity of a fluorescent flow discharge lamp of the characterdescribed may be obtained by using smaller electrodes, i.e., electrodesof smaller wire diameter, and by arranging them in such a manner that anessential portion of the length of the electrodes, and therefore anessential part of their glow discharge surfaces, is disposedsymmetrically with respect to the bowl end of the bulb and extendingportions of the electrodes extending in the di around the centerthereof, the glow discharge of the lamp having, simultaneously, arelatively high current density. The electrodes preferably are formeddirectly from the leading-in wires of the lamp, that is, they constituteextensions of the leading-in wires, and they are bent over in the formof hooks so that the inner end portions of the electrodes which sustainthe glow discharge extend in parallel side-by-side relation in adirection transverse to the bulb axis and are arranged approximatelysymmet1ically around the center of the bulb bowl.

The increase in luminous intensity of the glow lamp according to theinvention may be accounted for by the fact that, by diminishing the sizeof the glow electrodes, i.e., by employing electrodes of smaller wirediameter than customary heretofore, an increase in the current densityresults. This then produces an increase in the tempera-. ture of theelectrodes and of the gas filling of the lamp which, in turn, causes astronger or more etfective evaporation of the mercury in the lamp and,thereby, a higher ultraviolet output. The ultraviolet excitation of theinternal fluorescent coating on the lamp bulb is also much morefavorable by virtue of the concentration of the glow discharge surfacesof theelectrodes around the focus or center of the bulb bowl[ Theportions of the electrodes hearing or sustaining the glow discharge areadvantageously located a distance of about 2-8 mm., preferably 46 mm.,from the inner wall of the bulb bowl. In the case of well knownfluorescent glow discharge lamps used heretofore having plain linearwire type electrodes (i.e., not coiled or. annular electrodes), currentdensities up to about 0.4 ma./cm. of electrode surface have beenobtained, whereas by means of diminishing the size or wire diameter ofthe glow electrodes in accordance with the in-.

vention and, perhaps, also increasing simultaneously the glow dischargecurrent, current densities of more than 0.4 ma./cm. up to about 5ma./cm. of electrode surface may be obtained. If the wire electrodeshave a-wire diameter of 0.4 to 2.0 mm;, current densities of about 0.5up to 5 Ina/cm. of electrode surface are usually obtained. As is wellknown, for the purpose of rating the current intensity of the lamp therehas. to be taken into consideration, beside the glow dischargesustaining surface of the electrodes, also the particular design of theglow discharge lamp, more particularly its gas or vapor filling, the gasfilling pressure, and thekind of electrode material used, in order toprevent the occurrence of too much sputtering of the'electrodes' andconsequent darkening of the luminescentr'naterial; I

A furtherconcentration of the glow discharge electrode surface aroundthe center of the bulb bowl may be advantageously obtained by preventingthe longitudinally rection ofthe lampbulb axis from sustaining any ofthe glow discharge. For such purpose, the said longitudinally extendingportions of the electrodes must have a higher electronic work functionthan the hook-shapedbent over end portions of the electrodes which are.to sus-- tain-the glow'discharge. This result may be effected byproviding an insulation on the longitudinally extending portions of theelectrodes, as by means of a tightly applied, well adhering insulatinglayer of glass, silica paste or other suitable anti-glow material. Withsuch a construction, the glow discharge light is then concentratedparticularly to the bent over inner end or hook portions of theelectrodes which extend transversely to the lamp bulb axis around thecenter of the bulb bowl.

The accompanying drawing illustrates, on an enlarged scale ofapproximately 2: 1, various embodiments of fluorescent glow dischargelamps-according to the inven tion, shown without the conventional lampbase for purposes of simplicity. As shown, the glow discharge lampscomprise a sealed light-transmitting elongated or tubular glass bulb 1which is coated on its inner wall, more particularly on its generallyhemispherical bowl end 2, with a layer 3 of a suitable luminescent orfluorescent material which is responsive to mercury vapor excitation,e.g., such as zinc silicate or any of the phosphors commonly used inconventional type positive column fluorescent lamps in use at presentfor general lighting purposes. The bulb 1 is provided at its other endwith a reentrant stem press 4 in which is sealed a pair of lead-inconductors or wires 5, 6 which are formed with wire-type electrodeextensions or cold electrodes 7, 8 extending inwardly of the bulb fromthe stern press in a direction more or less longitudinally of the bulbaxis toward the bowl end 2 thereof.

In accordance with the invention, the electrodes 7, 8 are bent over, ata point near the bowl end 2 of the bulb l, to form laterally extendingportions 9, 10 which constitute an essential portion of the total lengthof the electrodes and which extend in parallel side-by-side relation ina direction transverse to the bulb axis. As shown, the

two spaced bent over electrode portions 9, 10 are formed from a simplelinear wire electrode instead of being welded to an electrode support asis usual in the case of disk or ring type electrodes.

If the wire electrodes 7, 8 have a wire diameter of 0.6

mm. and a length of 6 mm., there may be obtained, with an electrodesurface of about 0.233 cm. and a current intensity of 0.5 ma., a currentdensity of about 2.15 ma/crn. of electrode surface. The bulb diameter ofsuch fluorescent glow lamps may, for instance, amount to 12 mm. and thebulb length, including the base with built-in series resistance, may beabout mm. The wire electrodes 7, 8 preferably consist of nickel, butthey also may be made from any other suitable material, e.g., from ironor an iron-nickel alloy. The bulb 1 contains a filling of a suitableinert gas such as argon or a mixture of neon and argon and perhaps,helium, at a relatively low filling pressure of about 20 to mm. ofmercury. The

bulb 1 also contains a small quantity of mercury.

In the form of the invention shown in Figs. 1-3, the bent over portions9, 10 of the wire electrodes 7, 8 are of straight character and extendapproximately per pendicularly to the bulb axis. As an alternative, thebent over wire electrode portions may be of flattened V-shape, as shownat 11, 12 in Fig. 4.

In another form of fluorescent glow discharge lamp according to theinvention, the wire electrodes 7, 8 have a wire diameter ofapproximately 0.8 mm. and a length of approximately 12.0 mm. and thelongitudinally extending portions of the electrodes which extend in thegeneral direction of the lamp bulb axis are prevented from sustainingany of the glow discharge by means of a protective layer or coating 13of a suitable insulating or anti-glow material, such as a layer ofsilica paste for example, as shown in Fig. 4. In this case, only thelaterally extending or bent-over electrode portions 11, 12, having alength of for example about 6.0 mm., actually constitute the effectiveglow discharge sustaining electrode surfaces. With a glow lamp of suchconstruction, having an electrode surface of about 0.31 cm. and acurrent intensity of about 1.5 ma, it is possible to obtain, with acurrent density of about 4.85 ma./cm. of electrode surface, a materiallyincreased luminous intensity on the bulb bowl 2 as compared to thatheretofore obtainable.

It will be understood, of course, that while I have shown and describedrepresentative embodiments of my invention, the essential object of theinvention of providing increased luminous intensity on the bulb bowl ofa fluorescent glow discharge lamp, may be obtained by other arrangementsand dimensions of the electrodes 7, 8 and, if desired, of the lamp bulb,and also by using a diflerent filling gas or metal vapor, approximatelywithin the previously mentioned'limits.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A negative glow discharge lamp comprising a sealed light-transmittingbulb containing an inert starting gas at low pressure and a smallquantity of mercury, said bulb having a bowl end coated with aluminescent material, and a single pair only of closely spaced linearwire cold electrodes sealed into the end of the bulb opposite the saidbowl end thereof and sustaining therebetween the glow discharge in saidlamp, said wire electrodes having an essential portion of their lengthsextending in parallel side-by-side relation in a direction transverse tothe bulb axis and being disposed substantially symmetrically withrespect to the center of said bowl end.

2. A negative glow discharge lamp comprising a sealed light-transmittingbulb containing an inert starting gas at low pressure and a smallquantity of mercury, said bulb having a bowl end coated with aluminescent material, a pair of lead-in conductors sealed into the endof the bulb opposite the said bowl end thereof and extending thereintoin the general direction of the bulb axis, and a single pair only ofclosely spaced linear wire cold electrodes in said bulb sustainingtherebetween the glow discharge in said lamp, said electrodes comprisingextensions of said lead-in conductors and having an essential portion oftheir lengths bent over to extend in parallel side-by-side relation in adirection transverse to the bulb axis, said bent over electrode portionsbeing disposed substantially symmetrically with respect to the center ofsaid bowl end.

3. A fluorescent glow discharge lamp as specified in claim 1 wherein thesaid glow discharge surfaces of the electrodes are located a distance ofapproximately 2 to 8 mm. from the inner wall of the bulb bowl.

4. A fluorescent glow discharge lamp as specified in claim 2 wherein theportions of the said electrodes extending in the general direction ofthe bulb axis are provided with a protective coating of anti-glowmaterial to prevent the said electrode portions from supporting the glowdischarge.

5. A negative glow discharge lamp comprising a sealed light-transmittingbulb containing an inert starting gas at low pressure and a smallquantity of mercury, said bulb having a bowl end coated with aluminescent material, and a pair of linear wire electrodes in said bulbsustaining therebetween the glow discharge in said lamp, said electrodesbeing constituted of linear wire having a diameter of from 0.4 to 2.0mm. and being proportioned, with respect to the glow discharge operatingcurrent, to have a high current density greater than 0.4 Ina/cm. up toabout 5 ma./cm. of electrode surface, said elect-rodes having anessential portion of their lengths extending in parallel sideby-siderelation in a direction transverse to the bulb axis and disposedsubstantially symmetrically with respect to the center of said bowl end.

References Cited in the file of this patent UNITED STATES PATENTS2,298,581 Abadie Oct. 13, 1942 2,357,732 Ehrlich Sept. 5, 1944 2,402,019Carpenter June 11, 1946 2,564,040 Vance Aug. 14, 1951 2,824,255 MistlerFeb. 18, 1958 2,833,949 Driscoll May 6, 1958 2,838,707 Schwing et a1.June 10, 1958 2,843,805 Brodersen July 15, 1958 2,885,587 Wainio et a1May 5, 1959

